1. Field of the Invention
This invention relates to a high temperature SiC thin film thermistor using a sputtered SiC film as a temperature sensitive resistor. In particular, the thermistor can detect temperatures over a wide range of 0.degree.-500.degree. C.
2. Description of the Prior Art
There have been practically used many temperature sensors comprising metals, metal oxides and other materials. In a cooking oven with a pyrolytic self-cleaning function, there has particularly been desired a high performance temperature sensor. Since the above oven operates in the cooking temperature range of 50.degree.-300.degree. C. and in the pyrolytic self-cleaning temperature range of 450.degree.-500.degree. C., the temperature sensor is required to detect temperatures over a wide range of 0.degree.-500.degree. C.
Wires or films of Pt are one example of the most useful temperature sensitive elements. They are disclosed in U.S. Pat. Nos. 3,845,443, 4,222,025 and 4,375,056. Because of its superior thermal stability and higher accuracy, the Pt element can detect temperatures accurately over a wide range of 0.degree.-600.degree. C. However, it is disadvantageous in that its temperature sensitivity is low because of the low temperature coefficient of resistance, which is in the order of about 0.38.degree. %/C.
On the other hand, a conventional thermistor comprising a mixture of various metal oxides such as Fe, Ni, Co and the like is frequently used as a temperature sensor. This conventional thermistor has a high sensitivity, but, in general, its thermal stability is less than 300.degree. C. In addition to the metal oxide thermistor, there are various high temperature thermistors comprising a mixture of Al.sub.2 O.sub.3 and Cr.sub.2 O.sub.3, a pyrolytic polycrystalline SiC and others. They are described in U.S. Pat. Nos. 3,958,209, 4,086,559 and 4,208,449. These thermistors have good thermal stability in the higher temperature range above 500.degree. C. However, when they are used in the temperature range lower than 300.degree. C., resistance thereof becomes too high to be practically used because of their high B constant, which is more than 4000K.
Since the SiC thin film thermistor has a unique characteristic in that the B constant increases linearly with an increase of temperature in the range of about 2000K-4000K, as described in J. Phy. E, 15,520 (1982), it can detect temperature over a wide range. However, the thermistor can not operate at a high temperature of 500.degree. C. for a long time because of its poor thermal stability.